Generally, an eco-friendly vehicle includes a high voltage battery for supplying driving power and an auxiliary battery for supplying operation power to internal electrical apparatuses (e.g., electronic loads). In this case, a low voltage direct current (DC) to DC converter (LDC) connected to the auxiliary battery and the electrical apparatuses down-converts a high voltage of the high voltage battery into a voltage for charging the auxiliary battery to charge the auxiliary battery, when a voltage of the auxiliary battery does not exceed a reference value under a control of a higher controller.
The auxiliary battery serves to supply the operation power to the electrical apparatuses such as various lamps, systems, electronic control units (ECUs), and the like, as well as start the vehicle.
Up to now, a lead-acid storage battery has been mainly used as the auxiliary battery of the vehicle since the lead-acid storage battery may be recharged and be used even though the battery is completely discharged. However, the lead-acid storage battery is heavy and has a low charging density, and lead-acid used in the lead-acid storage battery is an environmental pollution material. Therefore, recently, the lead-acid storage battery has been replaced by a 12V lithium ion battery in an eco-friendly vehicle.
However, the 12V lithium ion battery may not be recharged when the 12V lithium ion battery is over-discharged. Therefore, in order to solve this fatal disadvantage, technologies of preventing over-discharge of the 12V lithium ion battery using a relay for preventing over-discharge have been continuously developed.
Meanwhile, in the eco-friendly vehicle, charging/discharging/maintenance of the auxiliary battery have been performed by controlling an output voltage of the LDC to be varied depending on a driving condition and a battery state. Particularly, in a state of charge (SOC) maintaining mode, an output voltage value of the LDC is set so that charging/discharging (e.g., charging or discharging) of the auxiliary battery are not generated.
However, charging/discharging currents of the auxiliary battery are not accurately adjusted to OA due to a deteriorated degree, a temperature, and the like, of the auxiliary battery, such that unnecessary charging/discharging are generated in the auxiliary battery.
Therefore, unnecessary energy loss of the high voltage battery is generated.